The genus Striga (Scrophulariaceae) in Africa

Twenty-eight species and six subspecies of the hemiparasitic genus Striga Lour., witchweed, occur in Africa. Twenty-two species are endemic. Witchweeds occur throughout the continent with greatest diversity in the grasslands and savannas north of the equator. Striga gesnerioides (Willd.) Vatke and S. hermonthica (Del.) Benth. have developed host-specific strains that may have distinct morphotypes. me accord these no formal taxonomic status. Striga hermonthica and S. asiatica (L.) Kuntze, limited to agroecosystems, may be recently derived from non-ruderal species. Striga hirsuta Benth. and S. lutea Lour., sometimes treated as conspecific with S. asiatica, are recognized as distinct species restricted to natural ecosystems. Striga linearifolia Hepper, with its strongly bilabiate corolla and perennial habit, is considered as a subspecies of S. bilabiata (Thunb.) Kuntze. Striga baumannii Engl. and S. fulgens Hepper are excluded from the genus. Striga baumannii has tuberous roots and a ligneous calyx and may represent a distinct genus. Striga fulgens, with free petals, is aligned with Chascanum E. Mey. in the Verbenaceae.